John Robert Schrieffer
1931–2019, Oak Park, Illinois, USA, Tallahassee, Florida, USA
American physicist who wrote down the BCS variational wavefunction of the superconducting state, completing the microscopic theory of superconductivity.
As Bardeen's graduate student at Illinois, Schrieffer sought a many-electron wavefunction embodying Cooper pairing. The ansatz he found — a coherent superposition over all pair-momentum occupations — immediately yielded the energy gap, the Meissner effect and the second-order transition of real superconductors. He later worked on magnetic impurities, surface physics and conducting polymers.
Nobel-winning work
Schrieffer's share of the 1972 Nobel Prize rested on the variational many-body wavefunction now bearing the BCS name. Written in 1957, it treats the superconductor as a coherent superposition of pair-occupied momentum states, with a single variational parameter per pair describing the amplitude of occupation.
Minimizing the energy produced the gap equation whose solution is the exponentially small gap Δ ~ ω_D exp(−1/N(0)V), explaining the isotope effect through the Debye frequency. From this state follow the Meissner effect, flux quantization and the thermodynamics of real superconductors.
Workplaces: University of Pennsylvania, Florida State University
United States